Monday, June 3, 2013

On 30 May 2013 the press reverberated with the news
that the Near-Earth Asteroid 1998 QE2, a monster “the size of nine ocean liners”,
was going to sail by Earth (without docking).This is a terrifying image: picture nine ocean liners falling from the
sky!What a splash that would make! And some sources say it is long as nine ocean liners,
and some say the width of nine ocean liners, and some say as big as nine ocean
liners…well, whatever.

Of course the comparison of an asteroid with an
ocean liner was motivated by the asteroid’s moniker (QE2), and should be
understood as poetic license, or at least as unlicensed poeticism.But is an asteroid of this size really a big
threat?True, it missed us by 5.8 million
kilometers THIS time, but its orbit will bring it back across Earth’s orbit over
and over again.We can’t guarantee we
will always be so lucky!

The realists among us will appreciate that the news
media routinely push the envelope of truth in order to generate scary
headlines.This is usually done by means
of liberal use of adjectives (huge, gigantic, etc.; strangely I haven’t seen
anyone refer to it as Titanic) rather than numerical facts.So, assuming we know about the existence and
usefulness of numbers, does QE2 represent a real threat? Good question… and thanks for asking!

1998 QE2 is in fact about 1.7 miles in diameter, a
pretty decent piece of rock, and has a 2000-foot satellite in orbit around it.Now, let’s see: 1.7 miles is about 2700
meters in diameter, or a radius of 1350 meters and a volume of 10.3
billion cubic meters.At an average
meteorite or asteroid density of 3 tonnes per cubic meter, this is 31 billion
tonnes.Now let’s compare it to a big
ocean liner—for example the Queen Elizabeth II:displacement 44,000 tonnes.So,
by the difficult mathematical operation known as long division, we see that
this asteroid (never mind its satellite) would deliver a mass equivalent to 700,000
ocean liners onto our unsuspecting heads. WHAT?The
sensationalist media have underplayed the
story by a factor of 80,000?

Why the disconnect?Because of the vague use of the word “size”.Some people use it to mean length, or area,
or volume, or mass.The length of an
asteroid tells little about the size of a threat it presents—unless, of course,
we know how to do arithmetic.

But the real measure of its potential for wreaking
havoc is its total kinetic energy.Let’s
take an impact speed of 16 kilometers per second as an example (many NEAs are
moving a lot faster than that).That
puts it in the million-megaton (1
teraton) league.That would be
comparable to 100 World War IIIs.

Tuesday, March 19, 2013

Not since 1910 have we been treated to so fine a year for
seeing comets.Don’t miss the chance to
see them yourself.Space.com has shown a
lovely photograph of two comets low in the western evening sky that should
inspire anyone to make the effort.Sadly, evening cloudiness over Puget Sound has denied me the opportunity—it’s
not quite as nice for astronomy on the Washington coast as it was in Tucson!

Where do comets come from?The simple answer, which the media pass on to us, is that they come from
the Oort Cloud, a vast swarm of dirty snowballs that orbit in random directions
around the Sun far outside the orbits of Neptune and Pluto.This explanation has the advantage that it is
sort or right—and the disadvantage that it is pretty inadequate.

Comets are usually divided into two families.First we have the long-period comets, which
typically take a million years to complete an orbit and spend most of their
time 10,000 AU from the Sun.These are
the Oort cloud comets.Their orbits are
quite close to random: about half are traveling the “wrong way” around the Sun.
which allows head-on collisions with planets at enormous closing speeds.Only those that approach to well within
Jupiter’s orbit ever get warm enough for wholesale evaporation of their ices,
which blows off vast streams of gases and dust that give comets their “hairy”
appearance, and hence the name “comet”, which comes from the Greek word for
hair.The overwhelming majority of the
Oort Cloud comets have never (“what, never?Well, hardly ever”) approached close enough to the Sun to light up, and
hence to be discovered.At best, such a
comet has been observed only once.

Occasionally a long-period comet will pass close enough to
Jupiter or Saturn to have its orbit strongly affected by the planet’s gravity.These comets are diverted into relatively
tame low-inclination orbits that cross the orbits of several of the terrestrial
planets, often with orbital periods of 3 to 7 years and with aphelia close to
the orbit of the planet that kicked it. These are the short-period comets, which may
be observed through dozens to hundreds of trips around the Sun.They pass by repeatedly on regular schedules
with well-known orbital periods, and for that reason are often called “periodic
comets”.

There are several other fates possible for an Oort Cloud
comet that ventures into our planetary system besides becoming periodic comets.Some, after a traumatic close encounter with
a giant planet, will be hurled outward at a speed well above the escape
velocity of the Sun and become lonely wanderers in interstellar space.The chances of such a body ever entering
another planetary system and getting close enough to its star to light up as a
bright comet are extremely remote.Space
is big, and stars are small.No comet
interloper from another planetary system has ever been observed.

But there are other fates in store for the long-period
comets.Some may fly by one of the giant
planets and be diverted into orbits that have low inclination and cross the
orbits of several of the giant planets.These bodies cannot avoid collisions or violent gravitational
interactions with these planets, and therefore have a short expected
lifetime.These bodies are called the Centaurs.They and a vast dynamically related group
called Trans-Neptunian Objects (TNOs), which, as their name suggests, orbit
near and beyond Neptune, can be both former and future comets.Pluto is one of the TNOs which happen to
belong to a subfamily of bodies that have reached an orbital accommodation with
Neptune, with a 3:2 orbital period resonance that prohibits them from ever
approaching Neptune closely or colliding with it. Bodies kicked into that neighborhood that were
not lucky enough to enter a safe resonant orbit would soon collide with
Neptune, be expelled from the Solar System, or become a Centaur.

In addition, the outer satellites of the giant planets,
those in retrograde orbits, are only very weakly bound to their planets.It is clear that these bodies may be captured
or lost into heliocentric orbits quite easily.Such a lost satellite may become a Centaur; a newly captured satellite
probably was a Centaur.

Periodic comets may make hundreds of perihelion passages
before the supply of volatile ices near their surfaces is exhausted.The body ceases to emit gases and dust,
cometary activity fizzles out, and we are left with an icy comet core that is
covered with a layer of fine, extremely black dust that not only blocks solar
heating of the interior, but also has a very low thermal conductivity.Once a dust layer a few meters thick has
developed, all cometary activity ceases and the body has the appearance of an
extremely dark (D-class) asteroid.Many
near-Earth asteroids (NEAs) not only follow orbits similar to those of the
periodic comets, but some have even been observed to make the transition from
comet to asteroid.If a small impact
event opens a hole in the dust blanket, solar heating can again reach the
buried ice and a “jet” of gas and dust can erupt.Many short-period comets are active thanks
solely to one or a few such local jets.And of course such a collision on a D asteroid may cause it to resume
cometary activity.Many NEAs that may be
dust-mantled icy cores of “extinct” comets can be recognized by their orbits
and their D-type reflection spectra. All
of these could again become comets.

The semantic distinctions between planetary retrograde
satellites, Centaurs, TNOs, long-period comets, periodic comets, and dark NEAs give
us useful ways of describing what and where a body is today, but they do not do
justice to the complex histories these bodies may have had before fitting
neatly into one of these convenient pigeonholes.

A Centaur may from time to time be perturbed into an Earth-crossing
orbit by one of the giant planets whose orbits they cross.Such a body, lighting up as it approached the
Sun, would then be termed a giant comet.The Centaur 10199 Chariklo is about
260 km in diameter, compared to 6 km for a typical large comet nucleus such as
the body whose impact ended the Cretaceous Era and extinguished the last of the
dinosaurs.An impact of Chariklo with
Earth would deliver about 100,000 times as much energy as that global
extinction event, equivalent to about 4000 tons of TNT for each person on Earth.That would be about 2000 times as severe as
an all-out nuclear World War III.Mankind would be extinguished and life on Earth would be set back to the
pre-Cambrian Era.

Unlike the dinosaurs, we have technologies that allow us to
find, track, predict, and even intercept potential impactors.It would be criminally negligent to ignore
the impact threat.

Friday, February 22, 2013

On 27 February Dennis Tito, who paid his way to the ISS as a
tourist back in 2001, will be announcing the plans of a new private space
company, the Inspiration Mars Foundation.
The rumor mill has it that their purpose is to launch a manned
expedition to Mars as early as January 2018.

According to several sources, the mission would be a 501-day
free-flying flyby (neither orbiting nor landing on Mars). It would be lifted into space by a Falcon
Heavy launch vehicle and with crew accommodation for two people in the form of
a modified Dragon capsule, of recent ISS fame.
This scheme would incorporate ideas already put forward by SpaceX’s Elon
Musk, who is a vocal advocate of both private space development and the
exploration and eventual colonization of Mars.

The mission would be financed privately and would advance on
a much more ambitious schedule than any governmental or intergovernmental
project could reasonably expect to achieve.

For those who instinctively disbelieve the concept that
private enterprise can provide access to space cheaper and on a larger scale
than governmental entities can, a refresher course on SpaceShipTwo, the Bigelow
inflatable space station module, the Dragon capsule, and the dozens of
companies that have set their sights on providing low-cost private access to
space would be in order.

This seems to be a typically American thrust, but in fact
Canadian, European, and other companies are also engaged in these
pursuits. In fiction, the first manned
mission to the Moon was envisioned by Jules Verne (De la Terre a la Lune; 1865)
as being a private venture funded by rich American industrialists, building on
Civil War military technology, and launched (fired!) from Florida by a giant
gun. In fact, strangely enough, the
first technically plausible suggestion of how to get humans into space was in a
novel, “Beyond the Planet Earth: In the Year 2000”, written by the pre-Soviet Russian
visionary Konstantin Tsiolkovskii in 1916.
In it, the impetus for the development of manned spaceflight came from an
international team of scientists and a group of private investors whom we would
now call venture capitalists.

Travel to Mars (“Barsoom”) was a standard theme of the
writings of Edgar Rice Burroughs. Percy
Gregg’s novel “Across the Zodiac” (1880) recounts a visit to Mars. Another early tale of interplanetary travel, like
Tsiolkovskii’s novel also set in the year 2000, was “A Journey in Other Worlds”, authored in
1894 by John Jacob Astor IV. These and
many other books, such as E. E. “Doc” Smith’s novels, generally attribute space
travel ventures to innovators and private individual, not governments.

Perhaps Dennis Tito’s announcement will bring that spirit of
non-governmental initiative not just into space, but all the way to Mars.

Thursday, February 21, 2013

We now have two competing companies with their sights set on
mining asteroids for commercial reasons.
Both companies are pursuing the dream I developed in my book, “Mining
the Sky”, and both companies include long-time friends and students on their
rolls. To me the fact that there is
competition in this endeavor is at least as important as the fact that it is
being done at all. It is through
competition that new ideas are stimulated and old ideas are put to the test.

Which of these companies is the wave of the future? I confess to having no crystal ball. Being near the head of the line is no
guarantee of long-term dominance—when’s the last time you used a Commodore PET
or a TRS 80, not mention an Apple I? Played
any games on your TI-99 recently? How’s
the market for Xerox Altos?

Huge sales do not even guarantee long-term success: the
best-selling personal computer ever was the Commodore 64, which, because of a
price war with the TI-99, drove all players to the brink of bankruptcy (or over
it).

The IBM PC and the Apple II were not “present at the
creation”: they were just better…and quite different in design philosophy. PCs and Apples still lead the personal
computer world, although IBM has long since sold its own PC business to Lenovo
in China, and armies of PC clones abound.

So are Planetary Resources Inc. and Deep Space industries
the TI-99s and Commodore 64s of the space mining endeavor? Or are they Apples and PCs? Tune in again in ten years and maybe we’ll
know.

A sure measure of the health of this new industry will be
when even more competitors appear.

I have seen asteroid mining referred to as a “billion dollar
industry”. This is not correct: if the
idea works, it is a multi-trillion dollar industry, making available to mankind
more resources than the human race has used to date. And if it is not successful, it will be known
as a multi-million dollar flop.

I’m betting on long-term success. Yesterday I joined the staff of Deep Space
Industries as their Chief Scientist. If,
as the researchers are telling us, working Sudoku and crossword puzzles helps
keep the brain functioning, then opening up the Solar System to the human race
is likely to be an even more stimulating endeavor. We no longer need fear “running out of
resources” on a “finite planet”.

Tuesday, February 19, 2013

First, it is undeniably true that humans are injecting
carbon dioxide and soot into the atmosphere at a record pace.The data are uncontested.Second, it is undeniably true that CO2
is a “greenhouse gas” which inhibits radiation of Earth’s surface heat into
space and thus has a global warming effect.Third, it is well established that water vapor has a far stronger
warming effect than CO2. As a
further complication, clouds made by the condensation of that water vapor can
lead to either cooling or heating, depending on the density, altitude, and
particle sizes in the clouds.Thus we
are forced to estimate what effect warming by CO2 will have on the
water vapor (and cloud) content of the atmosphere, a very difficult task.Fourth, we must also come to grips with the
warming effects of soot and carbon black, which also are products of human
origin via everything from biomass cooking fires to coal-fired power plants to diesel
engines.Fifth, we need to understand
all the correlates of natural processes such as solar variability and volcanic
dust emission. We can see clearly from
the data in the HADCRUT4 graph in the previous post (Global Warming Update) that
warming (and cooling) of Earth is far more complex than any one factor can
explain: attributing all the warming in any time interval to CO2
makes CO2 appear more important than it really is, and biases all
predictions in the direction of exaggerated warming.

Temperatures are influenced by the amount of radiation
absorbed by gases—but not in a linear fashion.The temperature increase caused by multiplying the abundance of a gas
such as CO2 by, say, a factor of two is called the “climate
sensitivity”: temperature is related to the logarithm of the absorbing gas
abundance.Doubling the CO2
abundance from the 19th-century level of less than 300 parts per
million (ppm) to about 600 ppm would have the same warming effect as doubling
the CO2 pressure again, to 1200 ppm.So what is this “climate sensitivity”?Climate modelers have used numbers ranging from about 1.5 to 6.5 oC
per doubling of CO2.Current
wisdom favors a number near 1.5 or 1.6, right at the very bottom of the range
used for generating dire climate predictions, for the short-term effects of
solar heating.

Prof. Berntsen in a previous post suggested that the rapid
warming of the 1978-1998 time period was due to a random combination of natural
factors, carbon dioxide warming, and soot warming.If we wrongly attribute all the observed
warming to CO2, we are led inevitably to a gross overestimate of its
warming power, predicting unreasonably high “climate sensitivity” and leading
computer models to exaggerate the future warming trend.If Prof. Berntsen’s estimate holds up, the
climate sensitivity of CO2 after taking out the effect of soot is
only about 60% of 1.5-1.6 degrees: call it 1 ºC.

How would we describe the temperature graph in the previous
post without making reference to theories and explanations?We could break the graph up into five “eras”:
1850 to 1927, with no significant net temperature change and a temperature
anomaly of -0.3 oC; 1927 to 1940, with a warming of about 0.3 oC;
1940 to 1978 with gentle cooling of 0.15 oC; 1978 to 1998 with a
strong warming of 0.65 oC, and 1998 to the present, with no significant
change.The “noise” in the data is
striking: there are many independent effects of similar size at work, which
sometimes work in synchrony.Of course,
if we included data extending back to the “Little Ice Age” of the 1600s, all of
the data on this graph would be termed “very warm”.And if we were to reach back to the “Roman
Warm Period” 2000 years ago we would find temperatures closely similar to those
of today.Going back 9000 years to the
early Holocene (the present interglacial period) we would have found an Earth
that was warmer than today without any human influence or record-high CO2
content, powered solely by natural variability.

It is sobering to realize that most of the “noise” in the
temperature graph is not random measurement errors, but real climate effects
that are not adequately treated in (and were not predicted by) present
models.But remember that, no matter how
complex our modeling of the atmosphere, some important factors such as volcanic
emission of dust and sulfur gases and the effects of the variability of solar
activity and solar wind strength will still defy prediction.

Climate modeling is one of the most difficult computational
problems known.Like any science, the
body of available data expands rapidly, and computer models must constantly be
updated to include those data.Many
effects, such as the role of clouds or of soot, or the variability of the Sun,
are recognized as important factors even while we still lack the detailed
quantitative understanding of them that we would need to incorporate them into
computer models.Critical thought is the
essence of science: we learn from experience and constantly improve our
theories in the light of new data.Similarly, theory points out what data we need to improve our
understanding, and may even suggest how to go about acquiring them.Skepticism is not the enemy of science; it is
the very heart of the scientific endeavor.

We need an end to name-calling and personal attacks and
threats.We need to remove the
discussion of global warming from the realm of politics and economically
involved interest groups of both extremes.We need to accept that anthropogenic global warming is not a “settled
science”, but a vigorous and ambitious area of research in which new knowledge
is of critical importance.Remember that
Newtonian physics was once a “settled science”: and then along came Einstein.For about a century, celestial mechanics was
also viewed as “settled science”: then along came spaceflight and modern
mathematics.Climate science is neither
“settled” nor “fraudulent”: we must stop repeating and amplifying the most
strident rhetoric, very little of which emanates either from scientists or from
those in the media with real understanding of the issues.We need less activism and more understanding.

There is one final very simple point to make: the phenomena
of nature are incredibly complex.Simplistic slogans such as “big industry is destroying our planet” and
“climate science is a left-wing plot” are not only ignorant; they endanger our
future.Let’s bury that simplistic rhetoric
and strengthen the science of complexity.

Monday, February 18, 2013

1.Yield:Current evidence suggests an explosive yield of a little less than 1
megaton of TNT, comparable to an ICBM warhead.We should be very grateful that it did not detonate closer to the
ground, or we would be looking at tens of thousands of civilian deaths.

2.Optimum burst height:The nuclear weapons literature, including the
classic 1977 analysis entitled The Effects of Nuclear Weapons, shows that the
effective range of destruction from an aerial explosion depends sensitively on
the altitude of the explosion.An
explosion at sufficiently high altitude strikes a very large area with a weak
shock wave, rattling windows but doing negligible damage.In the daytime, or in cloudy weather, there
may be no sightings of a fireball.A
little lower, and the same explosion would break windows.Glass shards accelerated by the blast wave
are the principal hazard.This is the
Chelyabinsk event.Move the explosion a
little closer to the ground, and radiant heating of the surface becomes
important.Fires can be ignited by the
flash, especially clothing, window curtains, and automobile upholstery.In rural areas, trees and brush ignite.This is the Tunguska event of 1908, which
flattened hundreds of square kilometers of forest and burned 2200 square
kilometers.A little closer to the ground,
and blast overpressures become high enough to cause structural failure of
reasonably well-constructed buildings.The “premature” failure of the factory building in Chelyabinsk probably
owes more to its Soviet-era construction quality than to the severity of the
blast.At about the same explosion
altitude, the air blast that follows the flash (traveling at the speed of sound
rather than the speed of light) hits hard enough to blow out many of the fires,
but potentially fanning others into a firestorm.In this sequence from high altitude to very
low altitudes, each successive blast strikes with greater intensity (higher blast
overpressure) over a smaller target area.A body that reaches the surface either intact or as a compact swarm of
high-velocity fragments can excavate a crater, depositing almost all of its
kinetic energy in an area about 100 times the actual area of the crater by
means of high-speed explosive ejection of debris from the crater.This is Meteor Crater in Arizona.Very large impacts eject vast quantities of
dust and vapor and shock-produced nitrogen oxides in the form of a mushroom
cloud, which lifts them to high altitudes and spreads them widely over the
Earth.The very biggest impacts seen in
the geological record actually blast away the atmosphere above a plane tangent
to Earth’s surface at the point of impact, hurling crater eject worldwide.This is the Chicxulub event at the end of the
Cretaceous Era, the famed dinosaur-killer.For a given explosive yield there is an altitude, called the “optimum
burst height”, at which the area of devastation is maximized.For a 1-megaton explosion the optimum burst
height is about 1700 meters (a mile) and widespread structural damage occurs
for any blast below about 5000 m (3 mi).For a 10-megaton explosion the optimum burst height is near 5000 m and
the threshold for structural damage is near 12000 m (7 miles).At yields of 1000 megatons (1 gigaton), a
10,000-year event, severe surface damage occurs at just about any plausible
burst height.

3.Entry Angle and Velocity:It is aerodynamic pressure that causes an
entering body to crush and shear itself into fragments.The aerodynamic pressure is proportional to
the density of the atmosphere and to the square
of the velocity.The density of the
atmosphere drops off roughly exponentially with altitude, and is therefore very
low at 100 km altitude.As a general
rule, bodies that enter at lower speeds penetrate deeper than those that enter at
higher (cometary) speeds.They contain
less kinetic energy per ton, but are more efficient at delivering that energy
to the ground.Bodies that enter the
atmosphere at shallow grazing angles (nearly horizontal motion) spend a
relative long time at high altitudes where the atmosphere is thin and crushing
is least probable.They tend to
decelerate rather gently and therefore are traveling slower at any altitude;
therefore they penetrate deeper before exploding than a vertically-entering
body of the same size and speed.Note
that, for any given material, the higher the velocity, the higher the altitude
of explosion: the faster the bullet, the less its penetration.There is also a huge range of strengths for
asteroidal and cometary material: cometary “fluff” fails at high altitudes;
iron meteorites (M-class asteroids) often penetrate all the way to the ground
before exploding, and hence deliver their full original kinetic energy to a
crater (or small cluster of craters) with high efficiency.This is the Sikhote-Alin meteorite fall in
eastern Siberia in 1947.

4.Linear Explosion:The energy dissipated by a strong, deeply
penetrating bolide is often released nearly in the form of a point explosion,
with almost all the original kinetic energy being given off in the same
moment.But many smaller bodies deposit
their energy along a lengthy path through the atmosphere as they break up in
many stages.This is especially true of
bodies with shallow entry angles.Since
the impactor may be traveling at 20 km per second, its speed is about Mach
30.We think of the shock wave from a
supersonic aircraft traveling at Mach 2 or 3 as a cone with an opening angle
of, say, 30 degrees originated at the nose of the aircraft.But at Mach 30 the opening angle is only
about 2 degrees: the energy released is very nearly in the form of a linear
explosion.Some theorists talk of the “exploding
wire” model, which is not a bad way to picture it.Imagine a “wire” stretching across the sky
that detonates nearly instantaneously.The first sound to reach you is not from the point where the explosion
began but from the segment of the wire nearest to you.That sound reaches you as a strong, sharp
blast, a “sonic boom”, after which the sound reaches you from ever more distant
locations on the wire.Thus after the
first sharp boom you hear simultaneously the noises emitted both before and
after the body passed closest to you.These explosions and “rumbling” continue until, at last, you hear the
first sounds given off during entry.The
first sounds, having traveled so much farther, reach you last.

5.Crater:There have been reports on the internet, some illustrated by photos of a
burning crater, that purport to show the impact point of the Chelyabinsk
bolide.The photos are simply a hoax,
showing file pictures of a natural gas fire that has been burning for decades
in an oil field in Kazakhstan.If there is an impact crater, it is a hole
found in the ice of a lake.That
suggests a low fire hazard.

6.Meteorites:Meteorite recovery from the bolide would be enormously valuable, and
this morning’s news claims over 50 stones recovered to date.My guess is that there is a potential for
recovery of hundreds or even thousands of stones, and that they will prove to
be ordinary chondrites (the most abundant types of meteorites, of H, L, and LL
classes).Much weaker (carbonaceous) material
would explode at high altitudes; strong (iron or stony-iron) meteorites could penetrate
to the ground intact and make a huge crater.Let’s keep our eyes on this: as the many images of the event are
carefully studied we should soon know the precise path of the bolide and hence
know where to look for any other meteorites it may have dropped.

7.Russian Defense Ministry Spokesman: A
high-ranking Russian military officer has been quoted as saying that “this was
no meteor; it was an American military test.”If you can see any military advantage to breaking windows in
Chelyabinsk, you’re more imaginative than I am.Also, Russian scientific sources are quoting entry speeds of 18-20
kilometers per second, which is far above entry velocity for return from the
Moon (about 11 km/s) and insanely larger than the top speed of any military
weapons system ever devised.The energy
content of the explosion suggests a mass of 10,000 tons, 100 times the lifting
ability of a Saturn 5 or the Space Shuttle (neither of which is in
service), and about equal to the displacement of a guided missile cruiser such
as the Ticonderoga.This officer would profit from conversing
with the Russian scientists who investigated the Tunguska event, and who
actually do know something about these events.Besides, if we take his explanation seriously, we would have to credit
those aggressive Americans with having had even higher technology in 1908.

Friday, February 15, 2013

Early today a huge aerial explosion rocked the Siberian city
of Chelyabinsk, collapsing or damaging buildings and shattering windows throughout
the city.Slivers of window glass
accelerated by the blast wave from the explosion sent at least 500 people to
hospitals for treatment, with many more injured less severely.The media are trumpeting a “meteor” explosion
and speculating about a link to this afternoon’s flyby of the Near-Earth
Asteroid 2012 DA14.I am being barraged
with requests for information, even though the amount of solid quantitative
date now available is minimal.Nonetheless, there are several points that can confidently be made.

1.This was
not a meteor.A meteor is an optical
phenomenon, a flash of light seen in the sky when a piece of cosmic debris (usually
dust- or sand grain-sized) enters Earth’s upper atmosphere, converts its huge
kinetic energy into heat, and “burns up” (vaporizes), usually at an altitude of
at least 100 km.The Chelyabinsk object
was a fragment of asteroidal or cometary origin, probably several meters in
diameter, properly called a “meteoroid” or, more loosely, a “small asteroid”.A brilliant fireball seen in the atmosphere
is called a bolide.Some bolides, caused
by entry of large pieces of hard rock, drop meteorites on the ground: a meteorite
is a rock of cosmic origin that reaches the ground in macroscopic pieces (not
dust or vapor).Some bolides are
cometary fluff, of which nothing is strong enough to survive as a meteorite.This body was fairly strong, and is therefore
more likely to be an asteroid-derived meteoroid.Indeed, some Russian sources are claiming
that a meteorite from the blast fell in a lake in nearby Chebarkul, Russia, but
this has not been verified.Such judgments
are tricky because the distance to the fireball is usually wildly
underestimated (“it cleared my barn, so it must have been at least 50 feet up”).

2.The path of 2012 DA14 is well understood.It is in a generally Earth-like orbit, except
that its orbit is inclined relative to the plane of Earth’s orbit around the
Sun.To first approximation, it is
neither “catching up with Earth” or “being swept up from behind by Earth”: Its
motion relative to Earth it basically at right angles to the direction of our
orbital motion.It will pass us from
south to north.Think of two cars on the
freeway traveling in the same direction at the same speed, one of them in lane
2 and the other switching from lane 1 to lane 3.Chelyabinsk is basically “behind the Earth”
as seen by the approaching asteroid.In
other words, the Chelyabinsk object is not associated with 2012 DA14.

3.There is also speculation about 2012 DA14 being
accompanied by debris and even small satellites.This is well founded, but these fragments, produced
by collisions of small rocks with the asteroid, must follow paths that are
closely similar to that of the parent asteroid.If they exist, and if they hit Earth, they will do so near or to the
south of the Equator.Incidentally, the
orbits of satellites of NEAs are usually close in, simply because distant
satellites will be stripped away by the tidal forces of the Sun (and now,
during a close flyby, by Earth also), and their orbital speeds are tiny
(centimeters to meters per second).

4.There was an early report of Russia scrambling
jet fighters to intercept the object.Here’s how that works: suppose the bolide is traveling at the absolute
minimum entry speed of about 10 km/second and radar picks it up at a range of
1000 km.This radar detection tells them
the speed of the bolide. From detection
to arrival they have 100 seconds, tops.Then they have the interesting task of intercepting something moving 10 (or
20) km/s with an airplane that has a top speed of, say, Mach 2.5.That’s about 0.75 km/s.See the problem?The real military significance of impact
airbursts is not that it is impossible to intercept them with jet aircraft: it
is the danger of a completely unpredicted high-yield aerial explosion occurring
over a major city in a heavily armed, politically unstable region: think, Tel
Aviv, Tehran, etc. Instant World War
III.

5.There’s a lot of talk and speculation about how
rare such events are.Any meaningful
statistics would require that we know how big it really was (the bigger the
rarer).But a reasonable first guess is that
this is a decadal object: ten per century hitting Earth, of which typically
nine are in sparsely populated or unpopulated areas, such as the Tunguska Event
of 30 June 1908 and the two Brazilian events around 1930.We’ll know more about the size and blast
energy soon. So my take is that these
events are not rare, but having one over a city is unusual.

In the
1997 edition of my book Rain of Iron and
Ice I included a lengthy table of reports from public media and scientific
journals documenting injuries, deaths, property damage, and near-misses due to
cosmic impact events, ranging from a meteorite knocking off a girl’s hat to a powerful
airburst showering a city in China with tens of thousands of stones and killing
over 10,000 people [Ch’ing-yang, Shansi, 1490 AD; source: Kevin Yao, Paul
Weissman, and Don Yeomans, Meteoritics29, 864-971 (1994)].My Monte Carlo models of the long-term
effect of impact events in my 2000 book Comet
and Asteroid Impact Hazards on a Populated Earth provide quantitative estimates
of the events occurring in hundreds of 100-year computer models.In it, Model H89 generates a low-altitude
airburst of 83 megatons yield at an altitude of 19 km.A random location generator placed this blast
over the city of Orleans, France, killing 40,000 people and igniting a
firestorm.After this model was published,
Pete Worden, who was then Commandant of Falcon AFB in Colorado Springs, sent me
an account that he had found in Bishop Gregory of Tours’ History of the Franks: “580
ADIn Louraine, one morning before the
dawning of the day, a great light was seen crossing the heavens, falling toward
the east.A sound like a tree crashing
down was heard over all the countryside, but it could surely not have been any
tree, since it was heard more than fifty miles away… The city of Bordeaux was
badly shaken by an earthquake… The city of Orleans also burned with so great a
fire that even the rich lost almost everything.”

Monday, February 11, 2013

In it we are treated to the spectacle of a CNN anchor
actually asking Bill Nye whether global warming can cause an asteroid
impact.

Is this the level of ignorance we should come to expect of
the media?I’m afraid it is.

Bill Nye, with astonishing self-control, did not break out
laughing at the absurdity.In his place,
I would have lost it…and maybe that would not have been a bad thing.

We have already had to listen to explanations of why cold
snaps and heavy snowfall are caused by global warming.What about the Dow Jones Industrial
Average?What about sunspots?The phases of the Moon?And what about fact-checking and editorial
oversight and minimal standards of scientific competence, such as completion of
a Junior High School general science course?

And I was just getting over the news, courtesy of the
Huffington Post and CNN, that Betelgeuse was about to explode and wipe us
out.(See my earlier post on “The Sky is
Falling!”)

Friday, February 1, 2013

I heard it clearly: CNN announced
that Iran had put a monkey in orbit.Several news sources also mentioned that the United States could not
confirm the story.So what’s the truth?

The truth is that CNN apparently
was hoodwinked by an astonishingly misleading press release from the Iranian
press agency, which used the word “satellite” to describe a mere probe.The Iranian launch was on a Kavoshgar 3 ballistic missile capable of
attaining 100 km altitude but far too slow to achieve orbital velocity.The monkey flew a parabolic trajectory that
reached 120 km altitude, but certainly did not circle the Earth.American radar and optical tracking stations
regularly monitor all satellite traffic, and infrared-sensing military
surveillance platforms in geosynchronous orbit high above the equator keep an
eye on all rocket launches.But neither
of these tracking systems is equipped with a monkey detector.Anything that gives off lots of heat is fair
game: bored staff members at USAF Space Command used to pass the time by
checking whether the trains on the Trans-Siberian Railroad were keeping to
their schedules.But a train gives off
far more heat than a monkey.

So why is 100 km altitude
considered “space”?The answer is quite
simple: 100 km is the lowest altitude at which a typical satellite can survive
for a single orbit against the retarding forces of air friction.Satellites with unusually large area (such as
a large expanse of solar cells) and low mass experience more drag deceleration,
and would not last for even one orbit at this altitude before reentering the
atmosphere and burning up.Compact,
dense satellites (such as those launched to study Earth’s gravitational field)
would last a little longer.But for
typical satellite designs, surviving one orbit (about 87 minutes) at 100 km
would be about normal.Besides, 100 is
such a nice, round number.

And what does “in orbit” mean?It means that the object is following a
ballistic (un-propelled) path that will take it all the way around a body such
as Earth or the Sun.For orbits around
Earth, that means at least a 40,000 km trip.The Iranian monkey launch traveled about 200 km, not 40,000, and briefly
reached a maximum altitude of 120 km.

Not that Iran can’t launch small
satellites: it has already done so three times, in 2009, 2011 and 2012.A real orbital mission with a monkey aboard
is a possibility for the future.The
remarkably uninformative press release by the Iranian press agency tells
nothing about the launch, but does mention that the purpose of this flight is
to prepare for manned spaceflight—and adds that the launch was in celebration
of Mohammed’s birthday. The Director of
the Iran Space Agency, Hamid Fazeli, recently announced that Iran plans to send
humans on “half-hour” space flights “within four years”.This is clearly not orbital flight, and I
expect that “half hour” will eventually be found to mean “quarter hour”.He also claimed that Iran will be ready for
manned orbital flight within 10 years.By then, the intrepid Iranonaut may find himself unnoticed among the
swarms of Western space tourists.

Who, if anyone, should care about
this monkey mission?Israel, which is
within reach of Iranian ballistic missiles such as the one used in this launch.

It has been nearly 40 years since human exploration of the
Solar System ended with the return of Apollo
17 to Earth.Space exploration at
that time was overwhelmingly dominated by the competition between the two Great
Powers, the Soviet Union and the United States.But we now live in a different era, in which several nations have
ambitious plans for their space programs and the Soviet Union is no more.

Here’s
how the future of Moon exploration looks from a February 2013 perspective.

The
first lunar mission in this coming decade will be NASA’s LADEE (Lunar
Atmosphere and Dust Environment Explorer) orbiter mission in August 2013.

The next lunar mission to fly after
LADEE will be the Chinese Chang’e 3
spacecraft, presently aiming for takeoff in October of this year.Chang’e
3 consists of a landing vehicle and a small rover, which can leave the
lander and explore the vicinity of the landing site.The last lunar landing was carried out by the
unmanned Soviet Luna 24 mission in
1976.Chang’e 3 is far more ambitious than even the recent Chang’e 2 mission, which orbited the
Moon for a year before departing via the Earth-Moon L2 Lagrange point for its
flyby of the near-Earth asteroid Toutatis
earlier this month.I will be in Beijing
to cover the Chang’e 3 mission live in
my role as a regular commentator on China Central Television.

Hard on the heels of the Chang’e 3
launch will be India’s Chandrayaan 2,
which will orbit and land on the Moon.The exact launch date of this mission is not yet firm, but a 2014 launch
is expected.Chandrayaan 2 was planned to deploy on the lunar surface, near the
lunar south pole, a small Russian-made rover, Luna-Glob 2, also referred to as
Luna-Resurs.It is presently
doubtful whether the Russian rover will be ready for the Chandrayaan 2 launch.The
name of the rover raises three obvious questions.First, “Glob” is not a description of an
amorphous or amebic space craft; it is the Russian word for “globe”.Second, this lunar rover is not based on the
Soviet-era Lunokhod rover designs of
40 years ago; it is a much more modern and smaller vehicle.And third, what about Luna Glob 1?Read on…

In 2015 we can expect the launch of China’s Chang’e 4 lander and rover.This mission, featuring increased rover autonomy, will extend the
technical scope of Chang’e 3.Also in 2015 the Russian Space Agency RKA
will launch the Luna-Glob 1
spacecraft into lunar orbit.Originally
planned for launch several years ago, this spacecraft was delayed by Russian
budgetary constraints.The highlight of
the mission as presently planned is the deployment of four penetrators (provided
by the Japanese Space Agency JAXA) which will impact the lunar surface at high
speed and return data on both the impact deceleration and the seismic activity
of the lunar interior.The orbiter will
study solar wind interaction with the Moon and the dust environment at orbital
altitudes, and also carry a cosmic ray experiment package.The very name of this mission is subject to
change: possibly due to financial constraints, it appears that this mission
will be divided into two parts, a lander to be launched in 2015 and an orbiter
in 2016.

The year 2017 may see the launch of
JAXA’s Selene 2, which was planned to
include an orbiter, lander, and rover.The orbiter is no longer included in the mission plan, and penetrator
probes one considered for the mission also appear to have been omitted.Several press reports have confused Selene 2 with a manned mission, which is
categorically nonsense.This mission had
been postponed for budgetary reasons, but now appears to be on schedule for a
2017 launch.

Also in
2017 we should expect the launch of China’s Chang’e
5 lander.This very ambitious
mission, which will drill 2 meters into the lunar surface, extract a core
sample, and return the sample to Earth, requires the availability of a new and
larger booster rocket, the Long March 5
(CZ-5).The first flight test of the Long March 5 is expected in 2014.

The
European Space Agency (ESA) has under consideration a lunar lander for flight
in about 2019, but budgetary debates have left the status of this mission in
doubt.Even more dubious are the Russian
Luna-Grunt 1 orbiter and lander and
the Luna-Grunt 2 lander with surface
sample return.The latter would, if
budgetary constraints allow, recapture the capabilities of the Luna 15 (?), 16, 20, 23 and 24 lunar sample return attempts of the
1970s, but with wholly new equipment.These missions are tentatively assigned to the 2020-2021 time
frame.The “Grunt” here is not a sound
effect, but the Russian word for “ground”, as in the ill-fated Phobos-Grunt mission of 2011-12, a
vehicle intended to land on and return a surface sample from the Martian moon
Phobos.Unfortunately, it ended up
exploring a subduction zone off the coast of Chile.

Monday, January 28, 2013

In October 2012 the Meteorological Office’s Hadley Center in
England, one of a handful of research centers that maintain global temperature
databases, released the HADCRUT4 data set, which shows no net global
temperature change since 1997.This is
in stark contrast to the clear temperature rise from 1968 to 1998, a change of
+0.7 oC in 20 years, for a warming rate of 0.035 oC per
year. The HADCRUT4 data can be seen at http://www.metoffice.gov.uk/hadobs/hadcrut4/figures/Figure7.png

The Met Office followed up this disclosure with a projection
of future warming trends (issued, strangely enough, during the Christmas
holidays, and consequently largely missed by the press).In it they predict what they call a
“continuation of global warming” over the next five years, reaching a
“temperature anomaly” of 0.55 oC by the year 2017. This phrase means
that the temperature increase in 2017 relative to the average base reference
temperature for the years 1961-1990 will be 0.55 oC.Somehow they neglected to mention that
the actual observed temperature anomaly has hovered around the +0.5 oC
level since 1998: in other words, it will not be significantly warmer in 2017
than it is now.From 1997 to 2017,
according to the Hadley Center’s best estimates, we will have had 20 years
without any global warming.

Last week Jim Hansen, a prominent climate modeler at NASA’s
Goddard Institute of Space Studies (GISS) in New York City, concurred with the
Hadley Center’s historical data.Dr.
Hansen was one of the earliest and most vocal proponents of the idea that human
activities, especially burning of fossil fuels, are responsible for global
warming.GISS also finds that the
“five-year running average” of global temperatures, spanning 14 years of data,
has not changed in the past decade.This
standstill in warming, which was not predicted by any of the climate models, reminds
us of the primacy of data over both enormously complex (but still
oversimplified) computer models and faith-based beliefs.It also presents a fresh challenge to climate
modelers.

Then, two days ago, Dr. Terje Berntsen, a professor at the
University of Oslo’s Department of Geosciences and a senior research fellow at
the Center for International Climate and Environmental Research in Oslo,
released a reassessment of the warming effects of carbon dioxide.His research, incorporating the data showing
the last decade and a half of no net global warming, revealed that the “climate
sensitivity” for carbon dioxide is about 1.9 oC per doubling of CO2,
far below the numbers often quoted in the media.

“Earth’s mean
temperature rose sharply during the 1990s. This may have caused us to
overestimate climate sensitivity,” Prof. Berntsen explains.“We were most likely witnessing natural
fluctuations in the climate system – changes that can occur over several
decades – and which are coming on top of a long-term warming.”Also recall that Prof. Ramanathan’s data
suggest that soot has two thirds as large a warming effect as CO2
does, so that 40% of the total warming should actually be attributed to soot.Then the climate sensitivity is only about
1.2 oC per doubling of CO2.Of course, the present temperature plateau
was not predicted by our models. Predicting the future effects of soot is hard
because controlling soot production is relatively easy compared to controlling
carbon dioxide release.Future soot
emissions from diesel engines and coal-fired power plants will reflect legal
and regulatory rules that do not yet exist, and which therefore defy
prediction.

We are reminded of the immortal words of that great
philosopher, Yogi Berra: “The trouble with predicting the future is that it is
very hard.”

Wednesday, January 16, 2013

The Curiosity
rover is preparing to drill a little hole in a slab of Martian sedimentary rock
to extract material for testing in the ongoing search for life on the red
planet.What can we expect to find?What was the environment like for the origin
and evolution of life forms on Mars?

We know
far more about the present physical and chemical conditions on the surface of
Mars than we know about the distant, presumably warmer and wetter, past.Since Mars has a thin, very dry atmosphere of
97% pure carbon dioxide, ultraviolet (UV) light from the Sun readily penetrates
to the surface.In the absence of more
than a tiny trace of oxygen, ozone cannot be made in quantity, and cannot
provide an ozone layer similar to Earth’s to protect the surface from killing UV
radiation. In fact, UV light can
dissociate carbon dioxide into carbon monoxide (CO) and atomic oxygen (O) even
at the surface of the planet.Even a
tiny trace of atomic oxygen is very bad news for organic matter: O is a very
powerful oxidizing agent.Any organic matter
exposed at the surface of Mars, whether exposed by weathering of ancient
organic-bearing sediments or dropped onto Mars by impacts of carbonaceous
meteorites, would quickly ”burn” into carbon dioxide and water vapor.It is only in the interiors of ancient
sedimentary rocks, where O cannot penetrate, that organic matter might
survive.

The CO2
content of the atmosphere of Mars is sufficient to provide an average pressure
of about 0.006 atmospheres at the surface, although this number is very variable
from place to place because of the wide range of elevations spanning a deep
basin (Hellas) and several towering volcanoes.The CO2 famous for maintaining Earth’s surface temperature
above the freezing point (via the greenhouse effect) has a surface pressure of
less than 0.0004 atmospheres.So why is
Mars so cold?Several reasons: the
greenhouse effect on Earth is dominated by water vapor, which is very rare on
Mars; Mars experiences about half the intensity of sunlight that Earth
receives.So an earlier, warmer Mars requires that it was also a wetter
Mars.You need water vapor to make Mars
warm enough to have water vapor!Given
favorable early conditions on Mars, with liquid water present and a strong
greenhouse effect at work, life may indeed have originated there.But what evidence of that former life would
we be able to find today?There are two
obvious possibilities: well-protected organic matter deep inside ancient sedimentary
rocks, or fossils of simple life forms.But evidence of ancient life would not necessarily prove an independent
origin for life off Earth: large impact events can launch surface rocks from
both Earth and Mars into orbits around the Sun, from which they can collide
with and land on either planet.Martian
life, if any, may be expatriate Earth life--- and vice
versa.

The story of the impact of carbon
dioxide (CO2) on climate is widely reported, but the media reports
often confuse matters needlessly by referring to CO2 as
“carbon”.In the real world, combustion
of both biomass and fossil fuels injects carbon dioxide, water vapor, and
incompletely burned carbon (soot, carbon black, or “black carbon”) into the
atmosphere.All three influence the
warming and cooling of Earth.Although
the strongest greenhouse effect of these three is due to water vapor, generally
the amount added by combustion is dwarfed by the natural background due to the
humidity of the atmosphere (although matters would be different if we flew
fleets of supersonic aircraft in the naturally dry stratosphere).Carbon (soot) has long been suspected as a
contributor to heat capture by the atmosphere.Dr. V. Ramanathan at Scripps Institution of Oceanography suggested back
in 2008 that, based on observational data, carbon black was almost as important
as CO2 in governing heat capture by the atmosphere. Climate modelers
generally dismissed his arguments, but the data continue to accumulate-- and
now we find in the latest issue of the Journal
of Geophysical Research that Dr. Ramanathan was right after all.In its coverage of this emerging story, the
Washington Post comments that “many researchers questioned his analysis because
it was based on observations rather than computer modeling”.And so it was.How shocking!

The process by which we favor
observational evidence over theoretical models has a name: it is called
“science”.We scientists revise our
models to conform to observation; it is grossly dishonest to reject observational
evidence simply because it fails to conform to current theories.Let us hope that the results of these
observations will soon be evident in improved computer modeling in which the
warming effects of carbon are better accounted for and the supposed impact of
CO2 on warming is proportionately reduced.Perhaps the anomalous leveling out of
observed global temperatures (observed
as opposed to predicted by models)
over the last 16 years can be better understood when the effects of soot are
properly accounted for. How important is
soot?The latest estimate is that it is
two thirds as important as CO2.So please, science writers, stop calling CO2 “carbon” and
start considering real carbon.It’s a
very big deal.

John S. Lewis

John S. Lewis is a professor emeritus of planetary science at the University of Arizona’s Lunar and Planetary Laboratory and is Chief Scientist at Deep Space Industries. His interests in the chemistry and formation of the solar system and the economic development of space have made him a leading proponent of turning potentially hazardous near-Earth objects into lucrative space resources. Prior to joining the University of Arizona, Lewis taught space sciences and cosmochemistry at the Massachusetts Institute of Technology. He received his education at Princeton University, Dartmouth College and the University of California, San Diego, where he studied under Nobel Laureate Harold Urey. An expert on the composition and chemistry of asteroids and comets, Lewis has written such popular science books as "Mining the Sky", "Rain of Iron and Ice", and "Worlds without End".